1. Field of the Invention
The invention relates to dry building material formulations comprising polymer powders, to methods for producing them and to their use for example as building material compositions, such as tile adhesives, reinforcing compositions or self-levelling compositions.
2. Description of the Related Art
Dry building material formulations comprise hydraulically setting binders, such as cement, and also fillers, polymers in the form of water-redispersible powders (polymer powders), and optionally other additives. Building material formulations find application for example as tile adhesives, joint fillers, filling compositions, grouts, renders or screeds. Prior to application, water is added to the dry building material formulations (fresh mortars). A diverse range of requirements is imposed on building material formulations. For instance, fresh mortars are to possess good processing properties, and the cured mortar compositions are to exhibit high mechanical strengths and strong adhesion to various substrates, such as to mineral substrates or to insulating materials, such as polystyrene panels, for example. In order to set an optimum profile of properties, therefore, specific additives are frequently added to the building material formulations.
For instance, US 2007/0256600 A1 recommends improving the adhesion of building material compositions to polystyrene substrates by adding phosphate esters. A disadvantage, however, is the high price of these additives. EP 0698586 A1 teaches the use of aromatic polyethers for these purposes. Environmental concerns have arisen against such compounds. DE 102010042 003 A, lastly, proposes the addition of polypropylene oxides or of ethylene oxide-propylene oxide block copolymers. These adjuvants, although leading to a considerable improvement in the adhesion, also result in poorer processing properties for the fresh mortars.
The use of aluminium silicates or silicas as anti-blocking agents for polymer powders is known and described in DE-2214410, for example. Polymer powders therein were produced by spray drying polymer dispersions. In the course of the spray drying, anti-blocking agents were introduced in solid form simultaneously with, but spatially separate from, the polymer dispersions, into the spray-drying device. For an analogous method, DE-A 3101413 recommends the use of hydrophobic silicas in solid form as anti-blocking agents. GB 929704 deals generally with the spray drying of polymer dispersions for the purpose of producing storage-stable, water-redispersible polymer powders, and for these purposes teaches, for example, the addition of protective colloids, such as polyvinyl alcohols, or of inorganic particles, such as calcium carbonate or silica. CN-A 101125946 describes water-redispersible polymer powders comprising polyvinyl esters, calcium carbonate and optionally organosilicones.
DE-A1 4124588 discloses the preparation of finely divided silica microdispersions by hydrolysis of silicic esters in aqueous ammonia solution, and also the use thereof in polymer dispersions for use in stone strengtheners. EP-A 0765899, finally, addresses the equipping of polymer powders with liquid adjuvants, by applying the liquid adjuvants to a support substance, such as highly disperse silicas, and then blending the supported adjuvants with a polymer powder.